91Ó°ÊÓ

The progression of the cell through the numerous checkpoints is ensured by positive cell-cycle regulators.

Proto-oncogenes are the genes that encode the positive cell-cycle regulators. What we call "proto-oncogenes" are genes that become oncogenes if they are mutated in the right manner.

Thus, the correct option is - (c).

Phosphorylation transfers ATP to substrates is carried out by kinases enzymes, which control the cell cycle. Protein kinases are enzymes that are inhibited by kinase inhibitors. So, these are not positive cell-cycle regulators.

Thus, option (a) is not correct.

Several genes encode negative regulator proteins, which when activated, prohibit the cell from undertaking uncontrolled division. Those are known as tumour suppressor genes. So, these are not positive cell-cycle regulators.

Thus, option (b) is not correct.

An oncogene is just a mutant (changed) version of a gene that seems to be essential for cell proliferation in the absence of cancer. They are the result of cell cycle negative regulation.

Thus, option (d) is not correct.